On Fri, 20 Oct 2017, Christoffer Dall wrote: Please Cc lkml when changing genirq core code. > It is currently unclear how to set the VCPU affinity for a percpu_devid > interrupt , since the Linux irq_data structure describes the state for > multiple interrupts, one for each physical CPU on the system. Since > each such interrupt can be associated with different VCPUs or none at > all, associating a single VCPU state with such an interrupt does not > capture the necessary semantics. > > The implementers of irq_set_affinity are the Intel and AMD IOMMUs, and > the ARM GIC irqchip. The Intel and AMD callers do not appear to use > percpu_devid interrupts, and the ARM GIC implementation only checks the > pointer against NULL vs. non-NULL. > > Therefore, simply update the function documentation to explain the > expected use in the context of percpu_devid interrupts, allowing future > changes or additions to irqchip implementers to do the right thing. > > This allows us to set the VCPU affinity for the virtual timer interrupt > in KVM/ARM, which is a percpu_devid (PPI) interrupt. I have a hard time to understand how adding the comment allows you to set VCPU affinity .... Thanks, tglx
